1. Field of the Invention
The present invention relates to LC noise filters, and more particularly relates to a laminated LC noise filter used for a high-frequency electronic circuit, a high-frequency signal transmission line, or other suitable devices.
2. Description of the Related Art
Conventional laminated LC noise filters include a capacitor portion having a layered arrangement of a plurality of insulating sheets provided with a capacitor electrode pattern on the surface thereof, and an inductor portion having a layered arrangement of insulating sheets provided with an inductor electrode pattern on the surface thereof. The capacitor portion and the inductor portion are layered and integrated. When these laminated LC noise filters are offered as products to users, they must be configured to have various cutoff frequencies fc in accordance with the needs of the users.
The cutoff frequency fc of the LC noise filter is determined by the inductance of the inductor and the capacitance of the capacitor, which are incorporated in the LC noise filter. Accordingly, in the conventional LC noise filter, to change the cutoff frequency, the inductance is changed by changing the number of the layered coil conductor patterns within the inductor. However, when the number of the layered coil conductor patterns is changed, the inductance of the layered coil conductor patterns is changed in specific increments, which consequently only allows the cutoff frequency fc to be set at these specific increments.
When it is necessary to precisely control the cutoff frequency fc, the inductance is changed by changing the shapes of the coil conductor pattern, or changing the magnetic permeability of the insulating sheet or the thickness thereof, whereby the cutoff frequency fc is precisely controlled. Alternatively, a desired cut-off frequency fcis obtained by changing the capacitance of the capacitor by changing the size of the area of the capacitor electrode patterns while the inductance is maintained constant.
However, the change of the shape of the coil conductor pattern, the change of the magnetic permeability of the insulating sheet, or the change of the thickness thereof requires a complicated and costly printing process to produce the coil conductor pattern or a complicated and costly manufacturing process to produce the insulating sheet. In addition, when the capacitance is changed while the inductance is maintained constant, the shape factor (the gradient of the insertion loss versus frequency characteristic) which pertains to the capability of separating signals from noise deteriorates. Furthermore, when the LC noise filter is used in high frequency ranges, the filter must have a small deviation in the cutoff frequency, which the conventional filter cannot achieve.
To overcome the above-noted problems with the prior art, preferred embodiments of the present invention provide an LC noise filter in which a desired cutoff frequency is easily and accurately achieved.
Preferred embodiments of the present invention provide an LC noise filter including a capacitor unit having a plurality of capacitor electrode patterns and a plurality of insulating layers that are stacked and integrated, and an inductor unit having a plurality of coil conductor patterns and a plurality of insulating layers that are stacked and integrated. In the LC noise filter, the inductor unit and the capacitor unit are stacked, and the cutoff frequency fc is adjusted in accordance with the distance d in the stacked direction between the coil conductor pattern and the capacitor electrode pattern that are next to each other in the stacked direction.
Since the capacitor electrode pattern is arranged in the vicinity of the inductor unit, eddy current loss is produced in the capacitor electrode pattern by the magnetic flux generated in the inductor unit. The eddy current loss changes according to the distance d in the stacked direction between the coil conductor pattern of the inductor unit and the capacitor electrode pattern in the capacitor unit that are arranged adjacent to each other in the stacked direction. The eddy current loss increases as the distance d decreases. When the eddy current loss increases, the inductance value of the inductor decreases. Therefore, adjusting the distance d causes the eddy current loss to be altered, and the inductance value is finely controlled to have a desired value.
Since the inductance of the inductor unit is finely controlled in accordance with the distance in the stacked direction between the coil conductor pattern and the capacitor electrode pattern which are next to each other, the desired cutoff frequency fc is obtained without using a complicated and costly manufacturing process or increasing materials for the insulating sheets. Therefore, an inexpensive LC noise filter is obtained having the desired cutoff frequency. Moreover, this LC noise filter produces minimal variations and deviations in the characteristic of the LC noise filter.
In the LC noise filter, the distance between the coil conductor pattern and the capacitor electrode pattern which are next to each other in the stacked direction, are preferably in the range of about 80 xcexcm to about 300 xcexcm. This enables the cutoff frequency to be effectively and accurately set.
In the LC noise filter, the distance in the stacked direction between the adjacent coil conductor patterns in the inductor unit is at least about 2.5 times as long as the distance in the stacked direction between the adjacent capacitor electrode patterns in the capacitor unit. With this configuration, the distance between mutually adjacent coil conductor patterns in the inductor unit increases and suppresses stray capacitance occurring among the coil conductor patterns.
In the LC noise filter, the relative dielectric constant E of the insulating layer is preferably in the range from about 50 to about 100. This prevents adverse influence of stray capacitance occurring across the input and output of the inductor, as well as enabling the capacitance of the capacitor to have a desired value.
Other features, elements, characteristics and advantages of the present invention will become more apparent from the following detailed description of preferred embodiments thereof with reference to the attached drawings.